Synchronizing device



April 30, 1946. MARTZT f I 2,399,421;

SYNCHRONIZ ING DEVI CE Filed Noy. 26, 1941 lN VENTOR BY M ATTORNEY Patented A r.- 30,1946

UNITED STATES PATENT OFFICE simcrmomzmd nsvioa Maurice Artzt, nadaonnem, N. 1., assignmto Radio Corporation of America, a corporation of Delaware Application November 20,1941. ml 42am 9' Claims. (01. rte-cos) ratus and the page'to be scanned, and further,

since at the reproducer this scansion must be exacthr duplicated, it is generally customary to transmit synchronizing signals which are indicative of the position of the scansion apparatus. Accordingly, it is one of the objects of my invention to provide an apparatus for controlling the speed of such a device in accordance with the time of receipt of the synchronizing signals.

It has been found that an induction motor may be used preferably with apparatus of this nature. Accordingly, it is another of the objects of my invention to provide a device for controlling the speed of an induction motor in accordance with the time of receipt of synchronizing signals.

In order to give an indication of the speed and phase of the scansion at the transmitter in a facsimile system, there is usually provided means for developing and transmitting a synchronizing signal which may be in the form of a steady tone indicating the speed of the scanner motor. Also, signals may be developed at the receiver which will give an indication of the speed and phase of the receiving and reproducing means. Accordingly, it is another of the objects of my invention to provide a device for comparing locally generated signals with signals received from an external source.

The comparison values which are developed by comparing the signal from an external source with the locally generated signal may be utilized to control the frequency of a wave generated at the receiver and which in turn controls the speed at which the induction motor'may be" operated.

paratus, and also coupled to the driving element of the induction motor is a means for developing electrical waves in accordance with the position of the rotor of the motor. The phase of the signals developed in this fashion are compared with the phase of a received tone such as a synchronizing tone and the resultant comparison wave/is utilized to aifect the frequenc of an oscillator, the wave developed y the oscillator being utilized to drive the induction motor.

My invention will best be understood by reference to the drawing, in which:

Fig. 1 shows a preferred embodiment thereof,

Figs. 2 and 3 are explanatory diagrammatic Referring to Fig. 1, there is shown a preferred embodiment of my invention. In this figure the induction motor is labeled, and is shown schematlcally by the windings l0 and H. The shaft of the induction motor is indicated by the dashed line It. Connected to the shaft is a tone wheel II which is positioned adjacent a magnet H, the

latter having wound thereabout a coil IS. The

actual apparatus driven by the induction motor has not been shown here since such apparatus is well known per se, and does not of itself comprise the essence of this invention.

It will be appreciated that the passage of the teeth in the tone wheel through the magnetic field in-the neighborhood of the magnet M will cause the development of a pulse each time a tooth passes therethrough. These pulses are indicated by a voltage e: which is shown as occurring between the conductors l8 and ii. A 300 cycle tone has been illustrated purely for illustrative purposes.

If it be assumed that the synchronizing signal or tone received is a 300 cycle tone, it will be apparent that if the apparatus remains in synchronism with the transmitting apparatus which gencrates a 300 cycle synchronizing tone, there will be a constant phase relationship between the two waves. The synchronizing tone has been indicated as being impressed across conductors i1 and I8, and is shown schematically as the voltage e1.

The voltage c1 and the voltage ea are impressed onto the primary Zll of a transformer having secondary 2|, and the combined voltages are illustrated by the symbol e3. Apparatus for receiving and segregating the synchronizing tone are well known per se and have not been shown here.

The voltage set-up across the secondary 2| of the transformer is impressed onto a full wave rectifier 22, this rectifier having-in the output circuit thereof a time constant circuit comprising resistance 23 and condenser 24, the cathode side of the tube 22 being grounded at 25. It will be appreciated, therefore, that there is provided in the output circuit of the tube 22 a direct cur-- rent voltage that varies in amplitude with the phase relationship between the two tones er and 62. This variable direct current potential is illustrated schematically as 6130, and is impressed onto the control electrode-cathode path of a thermionic tube 30 having an anode, cathode, and at least one control electrode.

An oscillating arrangement is provided comprising a thermionic tube 40 having anode 4|, cathode 42 and control electrode 43. The control electrode 43 is connected to the sliding arm of a potentiometer 44 having one terminal thereof grounded and the other terminal thereof con nected to a condenser 45, the latter in turn being serially connected with an inductive member 46 which has connected across a part of the windings thereof a condenser 41. The anode of the tube 30 is connected to the anode of the tube 40 through a resistor 50. The anode of the tube 40 is also connected to a common terminal of inductance 46 and condenser 41, which is remote from the terminal of inductance 46 which is connected to the condenser 45. This connection is accomplished through the conductor 49, and the anode supply is indicated schematically as +13 and is connected to the common terminal of inductanc 4B and condenser 41 which is nearest the connection of the inductance 45 to;the condenser 45. It will be appreciated, however, that this forms merely one form of oscillator'and that I am not limited to the specific form of oscillator shown.

It will be appreciated that the load on the oscillator will vary in accordance with the plate current of tube 30 and hence since th load will vary, the frequency of the oscillator will vary. A portion of the output of the oscillator is impressed through condenser onto a power am- .plifier illustrated schematically at 52. The output of the power amplifier is impressed onto the induction motor through leads 53 and 54.

Referring to Fig. 2, there is shown a diagrammatic set of waves whichillustrates the operation of the device when running synchronously. Since, for synchronous operation, the waves er and e2 will have the same frequency and hence will remain in constant phase relationship, e3 will be an unvariable wave. If this is true, then one will remain at a constant amplitude, and the average value of 6130 will not change, and hence the induction motor speed will not change.

Referring to Fig. .3, there is shown schematically the wave arrangement of the device when the motor slows down, for instance, and it will be seen that c1 and c2 pull apart in phase relationship and hence e3 varies. Since e3 varies, then eno will vary and the average value of em: will lower. This causes the tube 30 to draw more current and hence the oscillator load is changed and it will raise the oscillator frequency. When the tube 30 draws less current, as will be the case when the induction motor speeds up and er and c2 pull closer into a co-phasal relationship, epc will be greater in value and the tube 30 will draw less current, and the oscillator frequency will be lowered.

It is usually arranged that when the motor is running synchronously with the motor at the transmitter, enc averages about half value and the oscillator frequency is at the center of its range. Taking, for example, the increasing Ireasecnar quency oi the oscillator which takes place when the motor has slowed down, the increased trequency oi th supply allows the induction motor to run at a higher slip to carry an increased load. but the higher slip is furnished electrically rather than mechanically in the form or reduced speed.

This method of synchronism'also completely separates the synchronous tone from the motor frequency, and they do not have to be the same or even hear any direct relationship to each other. In actual tests the system has been shown to be very good, and is almost completely free from hunting tendencies.

It will be apparent that there may be departures from the particular showing which has been illustrated hereinbefore, but which will not depart from the spirit and scope of my invention, and accordingly I claim all such departures as may fal1 fairly within the spirit and scope of my invention as identified in the hereinafter appended claims. One example thereof is, for instance, the fact that a synchronous motor may be used in place of the induction motor, but the hunting characteristic is not quite as good as t at 01 the induction motor.

What I claim is:

1. The method of synchronizing the operation of a plurality of prime movers which comprises the steps of developing a signal representativ 0! a phase of the cycle or operation of each of said prime movers, comparing the developed signals, developing a signal representative of the comparison of the signals, and utilizing at least a portion of the signal representative of the comparison of the waves to control the speed or operation of at least one or said prime movers.

2. In an apparatus for synchronizing the movement of a prime mover with that of another prime mover, and wherein a signal is received indicative of the phase and speed of one 01 said prime movers, means for generating an electrical signal representative of the phase of the prime mover to be synchronized, means for combining the locally generated signal and the received signal, energy storage means, means for impressing onto said energy storage means energy proportional to the'instantaneous combined values of the received wave and the locally generated wave, and means for utilizing at least a portion of the stored energy to affect the speed of the prime mover to be synchronized.

3. In an apparatus for synchronizing the movement of a prime mover with that of another prime mover, and wherein a signal is received indicative of the phase and speed of one of said prime movers, means for locally generating a signal representative of the speedand phase oi the prime mover to be synchronized, means for combining the received signal with the locally generated signal, rectifying means, means for im pressing said combined signals onto said rectifying means, energy storage means electrically associated withsaid rectifying means whereby energy of a value proportional to the value of the combined received signal and locally generated signa1 is stored, oscillating means, and means for.

controlling frequency of oscillation of said oscillator in accordance with the value of the stored energy.

4. Apparatus in accordance with claim 3, wherein means are provided for impressing energy of a frequency dependent upon the irequency of oscillation of said oscillato onto aid prime mover to be synchronized to control the speed and phase thereof.

asamai 5. Apparatus in accordance with claim- 3. wherein said locally generated signal is generated by a tone wheel, and means for driving said tone wheel by said prime mover to be synchronized.

6. Apparatus in accordance with claim 3, where said prime mover comprise an induction motor.

7. In facsimile apparatus wherein scansion signal representative of the optical values oi a transmitted image are received as recurring trains of signals, and wherein synchronizing signal interspersed between said recurring trains of signals are received, means tor locally generat- 8 signals indicative of the speed and phase of the driving motor of said facsimile apparatus, means for developing a control potential representative of the instantaneous value and phase relationship 01' the combined synchronizing and locally generating signals, and means for utilizing said developed control potential to control the speed of the driving motor oi said facsimile apparatus.

8. Th methodot comparing the relative phase relationship of two alternating current waves or substantially identical frequency and of substantially constant amplitude, which comprises the molcombiningthetwowave toproducea resultant alternating current wave having a variable amplitude determined by' the phase displacement of the two waves, developing a uni-direcveloped pulsating current.

9. An apparatus for comparing the relative phase relationship of two alternating current waves or substantially identical frequency and of substantially constant amplitude, comprising mean for combining the two alternating current waves to produce a resultant alternating current wave having a variable amplitude determined by the phase displacement of the two waves, a rectiiier, means for applying the resultant alternating current wave to the rectifier to generate a uni directional pulsating potential oi. varying intensity, and iilter means for filtering the generated uni-directional pulsating potential to produce a direct current potential that varies in intensity in accordance with the phase relationship or the two original alternating current waves.

MAURICE ARTZT. 

